Scientific data on optical medium longevity.

Neil Maxwell wrote:
Unfortunately, this paper has very little hard scientific data on CDR
lifetimes behind it, though I believe their recommendations are mostly
valid. Still, they echo many bits of 'net wisdom with anecdotal
roots.


My opinion of this paper is even lower than yours.

Their timeline shows cassettes starting in the early 80s. Early 70s would
be more accurate. They claim punch card were in the 70s when it's a well
known technology from the early part of the century. It omits paper tape
and reel tape and vinyl and acetates and stuff I forgot.

One place says cdrs may use aluminum another place it says the opposite.

The 'solvent' thing is misleading. Water is a solvent. Any solvent dries
quickly and is gone. There's no reference for their caveat.

They claim polycarb absorbs moisture. Really?

Some jewel cases (their favorite) are clearly more dangerous than a paper
sleeve.

They offer data about about dvdr durability yet claim that cdr tests are
being developed. Huh?

I gave this just a fast read and already forgot several other quibbles. But
It's good enough for government work.

In article ,
wrote:
Neil Maxwell wrote:
Unfortunately, this paper has very little hard scientific data on CDR
lifetimes behind it, though I believe their recommendations are mostly
valid. Still, they echo many bits of 'net wisdom with anecdotal
roots.

My opinion of this paper is even lower than yours.
[...]
They claim polycarb absorbs moisture. Really?

quoting from:
http://palimpsest.stanford.
edu/byform/mailing-lists/av/2000/08/msg00063.html
-------------------------------------------------
To:
Subject: [AV Media Matters] The Permeability of Polycarbonate (PC)
used in optical co
From: Joseph Wrobel
Date: Fri, 25 Aug 2000 14:47:35 -0700
Message-ID:
-------------------------------------------------
For those of you who would like to learn more about the diffusion of
water into polycarbonate, I suggest you obtain a copy of the paper I
wrote that discusses the subject in depth: "Ramp profiles for optical
disc incubation", SPIE Vol. 2338 Optical Data Storage, 191-202, 1994.
Ed, you should be aware of this paper as it is referenced in the ANSI
standard for estimating life expectancy of CD-ROM (ANSI/NAPM
IT9.21-1996) and that for CD-R (ANSI/PIMA IT9.27-1999).

The purpose of the paper was to address the changes in polycarbonate
water content that occur as conditions are cycled during the high
temperature, high humidity incubations that are performed in
accelerated keeping studies of optical media using polycarbonate
substrates. As Ed points out, the rate of water diffusion in and out
of the polycarbonate substrate is very different at its two surfaces.
Water diffusion through the metal coated side is essentially nil;
water diffusion through the free polycarbonate surface, though slow,
is appreciable over the duration of an incubation experiment,
especially those run at high temperature.

The problem is not the moisture intake. The saturated moisture
content of polycarbonate at 20C is 0.3%; at 80C it rises only to 0.5%.
The problem is that unless due precautions are taken, when a disc held
at high humidity and high temperature for a long time is introduced
into a room environment, the moisture preferentially diffuses out the
free surface and, as it does, leaves behind a non-uniform distribution
of water in the substrate. Since polycarbonate expands when it picks
up water, the gradient in water content causes the polycarbonate
substrate to symmetrically deform ("bowl") to a spherical surface to
accommodate the gradient in expansion. If the gradient is extreme,
the disc deflection could exceed the CD deflection specification until
the disc equilibrates with the environment. And at room temperature,
this would take a rather long time, up to several days.
/quoting

For Kodak data, see:
http://www.cd-info.com/CDIC/Technolo...dia/Kodak.html


Cheers, Phred.

--
LID